Rotary cutting machines such as drill presses, lathes, and milling machines are well known. Such rotary cutting machines are commonly used to cut or remove metal from a workpiece, so as to provide a desired shape to the workpiece. For example, drill presses are typically used to form small to medium size circular openings in a workpiece; lathes are typically used to selectively reduce the diameter of generally symmetric, round workpieces; and milling machines are commonly used to selectively remove material from various shapes of work pieces, including the boring of larger circular openings therein.
Typically such rotary cutting machines are used to perform cutting operations upon metal workpieces. However, those skilled in the art will appreciate that various other materials such as plastics, polymers, and composites, may similarly be shaped. Rotary cutting machines typically comprise a spindle which is caused to rotate by an electric motor or the like. A tool holder attaches to the spindle and is configured to hold the cutting tool which has been selected so as to provide the desired cutting operation upon the workpiece. Generally, such tool holders comprise a central aperture which is configured to receive a shank or elongate shaft portion of the cutting tool. Typically, the tool holder is pulled into the spindle so as to securely hold the cutting tool in place with respect thereto.
Although such contemporary rotary cutting machines have proven generally useful for their intended purposes, the speed with which they operate tends to be undesirably constrained by vibration of the spindle, tool holder, and/or cutting tools associated therewith. More particularly, when either the rotational speed of the cutting tool, the rate at which the cutting tool is advanced with respect to the workpiece, or the depth of the cut being made is increased beyond limits defined by the material of the workpiece, then the cutting tool begins to chatter or vibrate undesirably in a manner which adversely affects the surface finish of the workpiece. Such vibration may also result in more substantial damage to the workpiece and/or the cutting tool if it is permitted to increase in magnitude and/or continues too long.
It will further be appreciated that such vibration of a cutting tool and/or tool holder may result in catastrophic failure of the cutting machine during high speed operations, thereby resulting in potential damage to the workpiece, equipment, and even possible serious injury of nearby personnel.
As those skilled in the art will appreciate, the above mentioned contemporary technique for attaching cutting tools to rotary cutting machines possesses deficiencies which detract from the overall utility of the rotary cutting machine. For example, such attachment of the cutting tool to the tool holder does not assure sufficient concentricity of the cutting tool with respect to the tool holder.
Such a lack of concentricity may result from many factors. For example, dirt, metal shavings, or other contaminants disposed upon either that portion of the cutting tool received within the tool holder or within the bore of the tool holder may cause the cutting tool to be mounted slightly off center. Further, normal manufacturing tolerances of the components of the tool holder may allow slightly off center mounting of the cutting tool.
As those skilled in the art will appreciate, such off center mounting of a cutting tool with respect to the tool holder results in an imbalance of the rotating system defined by the tool holder and the cutting tool. Even a very slight imbalance can cause vibration at high cutting speeds, i.e., high RPM settings of the rotary cutting machine.
As discussed above, such undesirable vibration of the cutting tool causes chatter, thereby resulting in degraded cutting performance, e.g., an undesirable finish of the workpiece and/or reduced cutting speed. Thus, it is desirable to provide for enhanced concentricity of a cutting tool with respect to the tool holder, so as to mitigate such undesirable vibration.
It would further be desirable to provide means for dampening vibration which occurs in the cutting tool and/or tool holder, so as to mitigate the undesirable effects thereof. For example, any vibration due to insufficient concentraticity of the cutting tool relative to the tool holder, as well as vibration from any other source, may be dampened so as to reduce the amplitude thereof, thereby mitigating the occurrence of undesirable chatter and facilitating cutting operations at higher speeds.